1. Field of the Invention
The present invention relates to a method for plugging a cell of a honeycomb structure and a method for manufacturing a honeycomb plugged structure, particularly to a method for plugging the cell in which plug portion having desired depth and/or desired shape can correctly and relatively easily be formed, and a method for manufacturing a honeycomb plugged structure using the plugging method.
2. Description of the Related Art
As shown in FIGS. 10(a) and 10(b), a honeycomb structure includes a plurality of cells 3 surrounded by partition walls 2 and extending through an axial direction, and has broadly been used as a catalyst substrate, filter, or the like. Depending on cases, especially in a case where the honeycomb structure is used as a filter, the honeycomb structure is used in the form of a honeycomb plugged structure in which some cells 3a are plugged by plug portions 4 as shown in FIGS. 11(a) to 11(c). These plug portions have heretofore been formed by charging ceramic slurry into desired cells and drying and/or firing the slurry (see JP-B-63-24731).
For example, when the honeycomb plugged structure is used as a filter for purifying exhaust gas of a diesel engine (hereinafter referred to as DPF), the body is sometimes exposed at a high temperature depending on the environments. Stresses such as a thermal stress are concentrated on boundaries between the plug portions and the cells, and it causes a possibility that cracks are easily made in the partition walls of the concentrated portions.
To solve such a problem, a filter has been proposed in which the boundaries between the plug portions and the cells is not in a linear or constant pattern (see JP-B-3012167). This feature has an effect of avoiding the concentration of the stress. However, in order to prevent the boundaries between the plug portions and the cells from having the constant pattern, an amount of the slurry to be charged in the cell needs to be changed for each cell, and this requires an excess steps. Even when the boundaries between the plug portions and the cells are formed in the constant or linear pattern, it has been difficult to form the plug portion having an exact depth in the conventional method.